Nihilistic view:

It is impossible to test if anything is conscious. To ask a thermometer to appreciate music is like asking a human to think in five dimensions. It is unnecessary for humans to think in five dimensions, as much as it is irrelevant for thermostats to understand music. Consciousness is just a word attributed to things that appear to make their own choices and perhaps things that are too complex for our mind to comprehend. Things seem to be conscient, but that is just because our morale tells us to believe in it, or because of our feelings for other things. Consciousness is an illusion.

Alternative Views:

One alternative view states that it is possible for a human to deny its own existence and thereby, presumably, its own consciousness. That a machine might cogently discuss Descartes' argument "I think, therefore I am", would be some evidence in favour of the machine's consciousness. However, if it discussed the proposition as a symbolic argument it would be all too human. The original proposition was an affirmation that conscious experience simply exists - we cannot deny it, because the denial is part of conscious experience. A conscious machine could even argue that because it is a machine, it cannot be conscious in the same way as a human being who had misunderstood the difference between symbolic argument and experience might argue this. Consciousness does not imply unfailing logical ability. The richness or completeness of consciousness, degrees of consciousness, and many other related topics are under discussion, and will be so for some time (possibly forever). That one entity's consciousness is less "advanced" than another's does not prevent each from considering its own consciousness rich and complete.

Today's computers are not generally considered conscious. A Unix (or derivative thereof) computer's response to the wc -w command, reporting the number of words in a text file, is not a particularly compelling manifestation of consciousness. However, the response to the top command, in which the computer reports in a real-time continuous fashion each of the tasks it is or is not busy on, how much spare CPU power is available, etc., is a particular if very limited manifestation of self-awareness and if we define consciousness as behavioural evidence of self-awareness this could be called consciousness.